On one machine (Mac), "convert foo.png ... -colorspace RGB foo.jpg" works, but on another machine (Linux) that gives me an all-black image. Conversely, on the Mac, -colorspace sRGB gives me an all-black image, and on the Linux machine that works.

As far as I can tell, both versions of ImageMagick were built the same way. Both machines are 64 bit. Both have lcms2.

WTF?

All I want is a portable incantation for my "convert" command-lines that says "don't ever give me CMYK JPEGs, because most browsers display those wrong." If there are other subtleties between "RGB" and "sRGB", I'm sure I don't care about them.